There are many uses for corrugated type, rectangular expansion joints. While the usual expansion joint is cylindrical, as it is easier to make and in the past has been more reliable, often gas carrying ducts are not circular but are square or rectangular. Thus, interconnecting gas tight, expansion joints are required to be square or rectangular.
In the past, such square or rectangular expansion joints have been made by making a pair of flat corrugated panels members, and then cutting the ends at a 45.degree. angle so that they mate into a corner. The mating edges are then welded. While this forms an expansion joint that can have a desired radius of curvature of the corrugations for flexing, the structure is weak at the weld points, which are not as ductal as the remaining metal. Thus, such expansion joints are subject to failure upon repetitive flexing. Further, such expansion joints are expensive to make.
Thus it is advantageous to have a corrugated corner for making square, rectangular or flat corrugated side expansion joints, that are integral throughout the sides and corrugated corners, and yet have a radius of curvature of the corrugations that allow repetitive successive flexing of the corrugations and the corner corrugations without failure.